Anaerobic digestion (AD) will play a major role in the future circular economy, in particular enabling biological closed loops with complete recycling of nutrients and improved recovery of energy. An emerging opportunity in urban environments is the integration of organic wastes treatment through AD and the re-use of digestate and nutrients in soil-less agriculture such as hydroponics.

This PhD project will look closer at these “waste to food” systems, and at the synergies that exist between the waste degradation and food production parts of the system. Activities will include the review of past attempts (e.g. the biological closed-loop for life support in space missions), the modelling of energy, water and nutrients flows and transformations in the different parts of the system, a model-based design and techno-economic evaluation of the system in different scenarios. Experimental tests may be conducted in laboratory environments, especially to evaluate the digestate-hydroponics interactions. The Energy 2050 group is currently collaborating with a successful micro-AD project in urban settings, and this will allow the student to be involved in a real case scenario.

Development and validation of control strategies for flexible and demand-driven anaerobic digestion

Bioenergy and anaerobic digestion can have a major role as a source of dispatchable energy in future energy systems with high penetration of intermittent renewables. The Energy 2050 group is involved in different research projects where a flexible operation of anaerobic digestion leads to an improved economy of the whole system. Examples of these projects are the provision of heat to autonomous desalination systems, the stabilisation of micro-grids in rural electrification projects, and the biomethanation of hydrogen from grid excess electricity (power to methane).

In all these scenarios an improved control of AD is necessary, which is able to match the biogas demand of the system while maintaining process stability. This project will involve the review of existing control strategies for AD, the use of process modelling to evaluate and benchmark the most appropriate control strategies for different demand-driven scenarios, and the experimental validation of the control strategies at laboratory scale.

Anaerobic co-digestion consists of the anaerobic digestion (AD) of a mixture of two or more substrates with complementary characteristics, so that biogas production, digestate characteristics and process stability are enhanced through their joint treatment. The Energy 2050 group is researching co-digestion for different scenarios, such as the digestion of energy-rich substrates to boost biogas productions in demand driven applications, or to improve the degradation of agricultural by-crops in rural digesters in developing countries.

This PhD project will systematically research the possible synergistic effects of co-digestion. These include the enhancement of organic matter decomposition due to the addition of easily degradable substrates (priming effect), the increased buffering capacity, the reduction of inhibitory causes, the provision of balanced micro and macro nutrients, the role of fibers as carriers of micro-organisms, the provision of optimal water content, etc. Modelling will be used to describe mechanistic interactions and design co-digestion strategies in different scenarios, which will be tested and validated with laboratory scale reactors.

Design and development of water desalination plants for rural communities, driven by a hybrid solar-biogas energy system

Freshwater supplies are becoming increasingly stressed as demand increases. Desalination technologies are able to produce drinking water from abundant resources such as seawater. Solar energy has been used extensively in water desalination applications, but a backup source is needed to ensure continued operation of the system during periods of low radiation. This project will investigate the integration of solar energy and biogas to provide heat and electricity to a community-scale desalination system. Several options for thermal and electrical integration exist, which will need to be analysed through a modelling approach and constrained by the socio-economic characteristics of the targeted communities. Polygeneration design methods, control optimisation and thermoeconomic evaluation may be used during the project. The research will benefit from one of our current academic international collaborations where a desalination pilot plant is in the process of being built.